Amazon RDS takes two DB snapshots during the upgrade process.The first DB snapshot is of the DB instance before any upgrade changes have been made.
In this case, the operating system is updated on the standby DB instance, and the standby DB instance is upgraded.To upgrade from your existing configuration to a supported SE2 configuration, use a supported upgrade path. If your DB instance uses a custom option group, in some cases Amazon RDS can't automatically assign your DB instance a new option group.For example, this occurs when you upgrade to a new major version.If your DB instance is in a Multi-AZ deployment, both the primary and standby replicas are upgraded.If no operating system updates are required, the primary and standby DB instances are upgraded at the same time, and you experience an outage until the upgrade is complete.For more information about the supported DB instance classes for each version and edition of Amazon RDS Oracle, see Choosing the DB Instance Class.
Before you perform a major version upgrade, Oracle recommends that you gather optimizer statistics on the DB instance that you are upgrading.
Gathering optimizer statistics can reduce DB instance downtime during the upgrade.
To gather optimizer statistics, connect to the DB instance as the master user, and run the Note Major version upgrades aren't supported for deprecated Oracle versions, such as Oracle version 184.108.40.206 and 220.127.116.11. A major version upgrade from 11g to 12c must upgrade to an Oracle Patch Set Update (PSU) that was released in the same month or later.
In all other cases, you must modify the DB instance manually to perform a minor version upgrade. The time for the outage varies based on your engine version and the size of your DB instance.
For information about what Oracle versions are available on Amazon RDS, see Oracle Database Engine Release Notes.
You must modify the DB instance manually to perform a major version upgrade.